Amid confirmation that 20 Americans have been diagnosed with the swine flu, officials at the U.S. Centers for Disease Control (CDC) said they fear death in the United States as they expect more cases of the virus to emerge.

Dr. Anne Schuchat, director of the CDC's National Center for Immunization and Respiratory Diseases, said it is premature to say the disease in the United States is different than the one that has killed about 86 people in Mexico, and how serious this new virus is compared to typical flu viruses remains to be seen. On Sunday, Canada became the third country to confirm human cases of the unique virus.

Earlier today, Department of Homeland Security Secretary Janet Napolitano said the government declared a public health emergency, which will allow it to free up resources to tackle the issue.

At a White House press conference, Dr. Richard Besser, acting director of the Centers for Disease Control and Prevention (CDC), ensured Americans that the administration is taking aggressive steps to control the outbreak, but that more cases are likely to expect to emerge in the near future.

"Flu viruses are very unpredictable. Outbreak of infectious diseases are very unpredicatable," Besser said. "We view this more as a marathon. We think this will continue to spread but we are taking aggresive action."

There is no vaccination for the swine flu strain, which has elements of pig, bird and human strains. But officials said they have ramped up medical surveillance around the country and as part of the emergency declaration, freed up state and federal resources for prevention. Officials also emphasized the importance of individual care and good hygenic pratices.

在确认 20 个美国人被诊断患猪流感之时，美国疾病控制中心（CDC）的官员们说，他们担心在美国发生死亡，因为他们预料会出现更多的这种病毒的病例。

美国疾病控制中心的国家免疫和呼吸系统疾病中心主任安妮 舒卡特博士说，说在美国的疾病不同于在墨西哥造成大约 86 人死亡的那种疾病，还言之过早；而且这种新病毒比较典型的流感病毒是如何的严重，仍有待观察。星期天，加拿大成为确认这种奇特病毒的人类病例的第三个国家。

今天早些时候，美国国土安全部秘书珍妮 纳波利塔诺说，政府宣布了突发公共卫生事件，这将使得政府能够腾出资源财力来解决这个问题。

在白宫举行的新闻发布会上，疾病控制和预防中心的代理主任理查德 贝瑟博士向美国人保证，政府正在采取积极的步骤控制疫情爆发，但是可能预计在不久的将来会出现更多的情况。

“流感病毒是非常难以预测的。传染病的爆发是非常难以预测的，”贝瑟说。“我们考虑这更象是一场马拉松。我们认为它将继续蔓延，但是我们正在采取积极的行动。 ”

还没有用于这种具有猪、鸟和人的菌株要素的猪流感病毒菌株的接种疫苗。但是官员们表示，他们已经加大了全国各地的医疗监察，并且作为紧急声明的一部分，腾出州政府和联邦政府的资源用于预防。官员们还强调了个人护理和良好保健习惯的重要性。